Full definition
A rectangular slot machined axially into a shaft and the bore of a hub (pulley, sprocket, gear, coupling) to receive a key — a small prismatic steel bar that prevents relative rotation between shaft and hub, transmitting torque through shear. Standard key dimensions per DIN 6885 (metric) and ANSI B17.1 (imperial) are specified as a function of shaft diameter. Common key materials: AISI 1018 or 1045 steel. The keyway reduces the effective shaft cross-section by approximately 25%, which must be accounted for in shaft strength calculations. Types: parallel key (most common), Woodruff key (curved, for tapered shafts), and gib-head key (for easy removal). Fit classes: normal (close sliding), close (interference), and free. Keyway machining methods: broaching (production), end mill (single pieces), or slotting.